Compressible products which are used in the building sector for thermal and acoustic insulation such as mineral wool products may be packaged at different stages in order to reduce the space such products occupy during storage and transport.
Mineral wool products such as glass mineral wool and rock mineral wool products may be packaged at a first stage with a primary wrap film. A compressible product such as a mineral wool mat may be rolled up in a roll packer together with the primary film and may be closed by an adhesive at the end of the roll up process to have finally a packaged mineral wool roll. In this process, a polyolefin film may be used as primary packaging material. Mineral wool slabs are packed in a different way: a polyolefin film is generally applied to the upper and lower surface of the slab or a pile of slabs before compression. A single mineral wool slab or a pile of multiple slabs may be compressed and the lower and upper film may be sealed at the front and back to close the package. The mineral wool slab or pile of multiple mineral wool slabs is then released from compression and is limited in expansion due to the holding force of the film.
During a secondary packaging stage, multiple previously packaged mineral wool rolls or slabs are compressed and pushed in a first and second sheet of film sealed at one end, and the package is closed by sealing the other end. The multiple mineral wool rolls or slabs are released from compression and are limited in expansion due to the holding force of the film. The obtained package is called a multipack. Sometimes, there is a tertiary packaging stage, where multiple multipacks are again compressed and pushed in a first and second sheet of film sealed at one end and the package is closed by sealing the other end. The multiple multipacks are released from compression and are limited in expansion due to the holding force of the film.
In the packaging stages, typically a polyolefin film is used whereby the thickness of the film depends on multiple factors including the compression ratio of the compressible product such as the mineral wool product. The film has to withstand high forces due the expansion force of the packaged rolls or slabs which are trying to revert to their original state. The creep of a film, i.e., the tendency of the film to elongate, generally decreases when the thickness of the film increases. However, for economical reasons and in order to comply with ecological requirements, it is desirable to keep the film as thin as possible.
Conventional non-oriented polyolefin films are used for packaging compressible products. For instance, EP 0908400 describes a mineral wool product compression-packaged in a film of polyethylene comprising high density polyethylene. However, these conventional non-oriented polyolefin films have high creep, i.e., high tendency to elongate, resulting in too high growing ratios of the packages. As a consequence, the compression ratios on the mineral wool are limited and rather thick films are to be used to compensate the poor creep properties.
The latest trend in packing mineral wool products is the use of machine direction oriented (MDO) films which can withstand high expansion forces in the machine direction. These existing MDO films have a low creep in the machine direction which leads to a very high tendency of the packaged product to stay in the compressed state. The existing MDO films have such low creep performance that even the thickness of the films can be reduced in comparison with the above mentioned conventional non-oriented polyolefin films. However, when using the existing MDO films for packaging a compressible product in a compressed state, a drawback of these films is their relatively poor heat sealing properties. For instance, sealing bars have to be well aligned and maintained with a lot of attention on a very regular basis, to get reasonable heat seals with these existing MDO films. But even when sealed on adapted sealing bars (e.g., Flexweld sealing bars from Qubiqa), the heat seals of the mineral wool packages prepared with the existing MDO films are fragile and form the weak point of the packaged compressible product. Mineral wool packs prepared with the existing MDO films are frequently popping open due to the poor sealing behaviour of these films.
Key in packing compressible products such as mineral wool products in a compressed state is to compress these products to a high degree to get a package with limited volume which can be stored and transported in an economical way, while being able to withstand the expansion forces of the packaged compressible product in the compressed state.
In view thereof, there exists a need for further and/or improved films and methods for packaging compressible products in a compressed state and/or packaged compressible products which comply at least partly with the aforementioned requirements and solve at least to a certain extent the aforementioned problems.